Field of the Invention
The present invention relates to an interrogation system for an airborne radar and a radar incorporating such a system.
Description of the Prior Art
In modern combat aircraft, it is now necessary to associate to the main search and tracking radar an interrogation system, known as identification friend or foe (IFF) interrogator, for making it possible to identify detected targets. It is therefore necessary to install two antennas in the nose of the aircraft.
A known solution consists of fitting the radar antenna and the interrogator antenna in such a way that there is minimum jamming between both antennas. According to a known solution, dipoles in vertical polarization for IFF transmission-reception are arranged in front of a slot antenna, a parabola, a non-deformable Cassegrain antenna radiating in horizontal polarization. The two antennas are mechanically connected and are therefore pointed and stabilized simultaneously. In this case, the protective radome of the antennas is adapted, for each frequency band of the radar signal and interrogation signal, by a network of conductor wires for the IFF band.
Although this solution is suitable for the interrogation signal, it leads to a reduction in radar preformance, a loss of gain and a rise in the relative levels of the minor lobes of the radar due to the interaction with the IFF dipoles and the network of radome adapting wires.
In the case of antennas having a rotating polarizer mirror, there is another possible solution for fitting the antennas, but this solution cannot be used for all antenna types and in the case of a Cassegrain antenna with a rotating polarizer mirror the perturbation caused by the IFF dipoles is unacceptable.